I've owned 7 Foci from new. 5 petrol and 2 diesel.
1.4 petrol is underpowered. 1.6 is much better. Zetec spec. is preferable, and also drives better due to uprated suspension, wheels and tyres, and better seats. I had a 2.5 ST last year, which was a magnificent drivers car, but was a tad expensive to buy and run
Diesel wise, the 1.6 TDCI engine with 110bhp is the one to go for. Be wary as some have a 90 bhp unit fitted. Check carefully. The power output is on the VLC. These engines are excellent, and are responsive, quiet, and very light on fuel. The 1.8 TDCI's are good too, but not as tax and insurance friendly. The old TDDI units are to be avoided. Crude units.
The choice depends on your driving. If you do under say 30,000 kms p.a. I reckon go for a 1.6 petrol.
I have a new one (a 3 door 1.6 Zetec Connection) and it's averaging almost 38mpg, which in the real world is excellent.